Dialing apparatus for power failure extension telephone set of key telephone system

Abstract

Disclosed is a dialing apparatus used for a power failure extension telephone set 30 in a key telephone system. The power failure extension telephone set 30 is driven by power supplied from a key service unit 2 so as to function as an extension telephone set when power is supplied to the key service unit 2, but directly connected to an office telephone line 1 so as to function as an individual telephone set when power is not supplied to the key service unit 2. The dialing apparatus comprises a dial switch 31 of single contact-layer structure and a control switch circuit 21 connected to the dial switch 31 and changed over according to the power supply or power failure condition of the key service unit. That is, when power is supplied to the key service unit 2, the control switch circuit 21 connects the dial switch 31 to a control circuit 19. This control circuit 19 is activated by power supplied from the key service unit 2 and detects the state of the dial switch to transmit a control signal to the key service unit. On the other hand, when power is not supplied to the key service unit 2, the control switch circuit 21 connects the dial switch 31 to a dial signal transmit circuit 20. This dial signal transmit circuit 20 is activated by power supplied through an office telephone line 1 and detects the state of the dial switch whenever a handset 16 is off-hooked, to transmit a call to the office telephone line 1.

What is claimed is: 
     
       1. A dialing apparatus for a power failure extension telephone set connected to a key service unit of a key telephone system, said telephone set being driven by power supplied through said key service unit in a power supply condition of said key service unit so as to function as an extension telephone set and being directly connected to an office telephone line in a power failure condition of said key service unit so as to function as an individual telephone set, comprising: a dial switch having a switch matrix of a single contact layer structure;   a control switch circuit connected to said dial switch and switched according to said power supply condition or said power failure condition of said key service unit;   a control circuit, activated by power from said key service unit in said power supply condition of said key service unit and connected to said dial switch via said control switch circuit, for detecting a state of said dial switch to transmit a control signal to said key service unit; and   a dial signal transmit circuit activated by power through said office telephone line in said power failure condition of said key service unit and connected to said dial switch via said control switch circuit, for detecting a state of said dial switch to transmit a call to said office telephone line.   
     
     
       2. The dialing apparatus of claim 1, wherein said switch matrix comprises a plurality of switches for mutually connecting plural column signal lines and plural row signal lines, respectively; said column signal lines being connected to both said control circuit and said dial signal transmit circuit; said row signal lines being selectively connected to said control circuit or said dial signal transmit circuit via said control switch circuit, according to said power supply condition or said power failure condition of said key service unit; said control circuit and said dial signal transmit circuit detecting a state of said dial switch by checking the mutual connection relationship between said column signal lines and said row signal lines; and isolating elements located in said column signal lines to electrically isolate said control circuit from said dial signal transmit circuit or vice versa. 
     
     
       3. A power failure extension telephone set connected to a key service unit of a key telephone system, said telephone set being driven by power supplied through said key service unit in a power supply condition of said key service unit so as to function as an extension telephone set and directly connected to an office telephone line in a power failure condition of said key service unit so as to function as an individual telephone set, comprising: a dial switch having a switch matrix of a single contact layer structure;   a first control switch circuit connected to said dial switch and switched according to said power supply condition or said power failure condition of said key service unit;   a control circuit, activated by power from said key service unit in said power supply condition of said key service unit and connected to said dial switch via said first control switch circuit, for detecting input signals from said dial switch to transmit a control signal to said key service unit;   a dial signal transmit circuit, activated by power through said office telephone line in said power failure condition of said key service unit and connected to said dial switch via said first control switch circuit, for detecting input signals from said dial switch to transmit a call to said office telephone line;   a second control switch circuit connected to a microphone and an earphone and switched according to said power supply condition or said power failure condition of said key service unit;   a speech circuit, activated by power from said key service unit in said power supply condition and connected to said microphone and said earphone via said second control switch circuit, for connecting said microphone and earphone to said key service unit; and   a telephone circuit, activated by power through said office telephone line in said power failure condition of said key service unit and connected to said microphone and said earphone via said second control switch circuit, for connecting said microphone and said earphone to said office telephone line.   
     
     
       4. The power failure extension telephone set of claim 3, which further comprises: a connection line provided between said telephone set and said key service unit, for supplying power from said key service unit to said telephone set in said power supply condition of said key service unit and supplying power from said office telephone line to said telephone set in said power failure condition of said key service unit;   a first power supply circuit for supplying power to both said speech circuit and said control circuit;   a second power supply circuit for supplying power to said dial signal transmit circuit; and   a distributing circuit connected to said connection line, for selectively distributing power supplied through said connection line to said first and second power supply circuits according to said power supply condition or said power failure condition of said key service unit.   
     
     
       5. The power failure telephone set of claim 4, wherein said distributing circuit is a relay switch for selectively connecting said connection line to said first and second power supply circuits, according to said power supply condition or said power failure condition of said key service unit. 
     
     
       6. The power failure telephone set of claim 4, wherein said distributing circuit comprises a first transistor switch for connecting said connection line to said first power supply circuit in said power supply condition of said key service unit, and a second transistor switch for connecting said connection line to said second power supply circuit in said power failure condition of said service unit.